Transcript

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Section 3Storage Devices and Media Jon Spavin

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Magnetic drum memoryInvented all the way back in 1932 (in Austria), it was widely used in the1950s and 60s as the main working memory of computers. In themid-1950s, magnetic drum memory had a capacity of around 10 kB.Above left: The magnetic Drum Memory of the UNIVAC computer.Above right: A 16-inch-long drum from the IBM 650 computer. It had 40tracks, 10 kB of storage space, and spun at 12,500 revolutions per minute.

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The hard disk drive. The first hard disk drive was the IBM Model 350 DiskFile that came with the IBM 305 RAMAC computer in 1956. It had 50 24-inchdiscs with a total storage capacity of 5 million characters (just under 5 MB). Above: IBM Model 350, the first-ever hard disk drive.

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The first hard drive to have more than 1 GB in capacity was the IBM 3380 in1980 (it could store 2.52 GB). It was the size of a refrigerator, weighed 550pounds (250 kg), and the price when it was introduced ranged from $81,000 to$142,400.Above left: A 250 MB hard disk drive from 1979. Above right: The IBM 3380from 1980, the first gigabyte-capacity hard disk drive.

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The floppy discThe diskette, or floppy disk (named so because they were flexible), was inventedby IBM and in common use from the mid-1970s to the late 1990s. The first floppydisks were 8 inches, and later in came 5.25 and 3.5-inch formats. The first floppydisk, introduced in 1971, had a capacity of 79.7 kB, and was read-only. A read-write version came a year later. Above left: An 8-inch floppy and floppy drive next to a regular 3.5-inch floppy disk. Above right: The convenience of easily removable storage media.

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Magnetic tapeMagnetic tape was first used for data storage in 1951. The tape device was calledUNISERVO and was the main I/O device on the UNIVAC I computer. The effectivetransfer rate for the UNISERVO was about 7,200 characters per second. The tapeswere metal and 1200 feet long (365 meters) and therefore very heavy. Above left: The row of tape drives for the UNIVAC I computer. Above right: The IBM 3410 Magnetic Tape Subsystem, introduced in 1971.

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Section 3 – Storage Devices• Backing up data – What is Backing Up? – Why do we back up?

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Section 3 – Storage Devices• (3.1) Backing up data – What is Backing up data? • Copying of files and data to a different medium (disk, tape, flash drive, etc,) in case of a problem with the main storage device. • Some backups are often stored in a different place to the main storage. – Why do we back up? • Data could be lost • Hackers could be responsible for the corruption or even loss of data • Backups are also made in case the file need to be used elsewhere. The original file are then protected against possible corruption or loss

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(3.1) Backing up data What is Backing up data?• Copying of files and data to a different medium. – Can you identify at least three different types (disk, tape, flash drive, etc,) in case of a problem with the main storage device. •Some backups are often stored in a different place to the main storage. •Can you identify a number of different places?

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Section 3 – Storage Devices• (3.2) Types of Access – Serial Access • With this system, to access the data it is necessary to start at the beginning and then access each piece of data in turn until the required information is found. – Direct Access • This method is used with magnetic disks and with optical media. The computer uses a key field to calculate where the data has been stored.

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(3.1) Types of Access Types of Access?• Serial Access – With this system, to access the data it is necessary to start at the beginning and then access each piece of data in turn until the required information is found. •Direct Access This method is used with magnetic disks and with optical media. The computer uses a key field to calculate where the data has been stored.

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How does the Hard Drive work?• Theres just a large shiny, circular "plate" of magnetic material called a platter, divided into billions of tiny areas. Each one of those areas can be independently magnetized (to store a 1) or demagnetized (to store a 0). Magnetism is used in computer storage because it goes on storing information even when the power is switched off. If you magnetize a nail, it stays magnetized until you demagnetize it. In much the same way, the computerized information (or data) stored in your PC hard drive or iPod stays there even when you switch the power off.

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What are the parts in a hard drive?1. Actuator (compact electric motor that moves the read-write arm).2. Read-write arm swings read-write head back and forth across platter.3. Central spindle allows platter to rotate at high speed.4. Magnetic platter stores information in binary form.5. Plug connections link hard drive to circuit board in personal computer.6. Read-write head is a tiny magnet on the end of the read-write arm.7. Circuit board on underside controls the flow of data to and from the platter.8. Flexible connector carries data from circuit board to read-write head and platter.9. Small spindle allows read-write arm to swing across platter.

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Hard DrivesLittle and large: Heres the 30GB laptop hard-drive (shown in the other photos onthis page) next to a 20GB PCMCIA hard drive from an iPod. The two drives lookstrikingly similar and work exactly the same way (both are made by Toshiba), butthe iPod drive is even more of a miracle of miniaturization!

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Backing Storage Media• All computer systems have come equipped with some form of backing storage. When a user type data into a computer, the information is stored temporarily on the RAM – however, this information would be lost as soon as the computer was turned off. Backing storage devices ensure the data is stored permanently and can be used later. – Either internal or External and one of three types • Magnetic • Optical • Solid State